The entire disclosure of Japanese Patent Application No. Hei 11-299718 filed on Oct. 21, 1999, including the specification, drawings and abstract, is incorporated herein by reference in its entirety
1. Field of the Invention
This invention relates to a pulse tube refrigerator and, more particularly, to a pulse tube refrigerator for cryogenic refrigeration.
1. Description of Related Art
A pulse tube refrigerator is useful as a cryogenic refrigerator. The pulse tube refrigerator refrigerates working fluid by oscillating the working fluid while shifting the phase of the pressure oscillation and displacement of the working fluid.
Various pulse tube refrigerators of this kind have been proposed, for instance by Yuan and J. M. Pfotenhauer xe2x80x9cA single stage five valve pulse tube refrigerator reaching 32Kxe2x80x9d, in Advances in Cryogenic Engineering, Vol. 43, (1998), P.1983. FIG. 5 is a block schematic diagram of the pulse tube refrigerator introduced in the above-mentioned publication. This pulse tube refrigerator 80 comprises a pressure oscillator 81 and a refrigerating portion 82.
The pressure oscillator 81 generates pressure oscillation to the working fluid filled in the pulse tube refrigerator 80 and comprises a compressor 83, a first high pressure supply on-off valve 84, a first low pressure supply on-off valve 85, a second high pressure supply on-off valve 86 and a second low pressure supply on-off valve 87. An outlet port of the compressor 83 is connected to both ends (left side and right side as viewed in FIG. 5) of the refrigerating portion 82 via the first high pressure supply on-off valve 84 and the second high pressure supply on-off valve 86 respectively. An inlet port of the compressor source 83 is connected to both ends of the refrigerating portion 82 via the first low pressure supply on-off valve 85 and the second low pressure supply on-off valve 87 respectively. The pressure oscillator 81 generates pressure oscillations in the working fluid (gas) in the pulse tube refrigerator 80 (refrigerating portion 82) by controlling the opening and closing of the first and second high pressure supply on-off valves 84, 86 and the first and second low pressure supply on-off valves 85, 87 at a predetermined timing.
The refrigerating portion 82 comprises a regenerator 91, a low temperature heat exchanger 92, a pulse tube 93 and a high temperature heat exchanger 94 connected in series in-line. A hot end of the regenerator 91 is connected to the pressure oscillator 81 via first high and low pressure supply valves 84 and 85. A cold end of the regenerator 91 is connected to the low temperature heat exchanger 92. The regenerator 91 gradually refrigerates the working fluid while the working fluid moves therethrough towards the low temperature heat exchanger 92 side and gradually heats the working fluid moving therethrough towards the pressure oscillator 81 side.
The low temperature/heat exchanger 92 connected to the cold end of the regenerator 91 generates a low temperature. In order to effectively remove the heat of a device to be refrigerated, such as an electronic device, in contact with the low temperature heat exchanger 92, the low temperature heat exchanger 92 is provided with a number of holes regularly formed along the flow direction of the working fluid.
The pulse tube 93 connected to the low temperature heat exchanger 92 is formed by a hollow tube having a cold end 93a on the low temperature heat exchanger 92 side and a hot end 93b on the high temperature heat exchanger 94 side. The pulse tube 93 is made of a material with low heat conductivity in order to prevent the transfer of the heat generated by the oscillation from the hot end side to the low temperature heat exchanger 92.
The high temperature heat exchanger 94 connected to the pulse tube 93 includes a number of holes regularly arranged along the flowing direction of the working fluid. The high temperature heat exchanger 94 cools the hot end side by releasing the heat of the working fluid flowing therethrough to the outside thereof. The high temperature heat exchanger 94 is connected to the second high and low pressure supply on-off valves 86 and 87.
The pressure oscillation of the working fluid in the pulse tube 93 is generated by controlling the opening and closing of the first high and low pressure supply valves 84 and 85 at a predetermined timing. The pressure oscillation of the working fluid in the pulse tube 93 is auxiliary generated by controlling the opening and closing of the second high and low pressure supply on-off valves 86 and 87 at a predetermined timing to adjust the phase lag between the phase of the pressure oscillation and the displacement of the working fluid in the pulse tube 93 of the pulse tube refrigerator 80. The working fluid (gas) is moved in one direction to release the heat at the high temperature heat exchanger 94 and moved in the other direction to absorb the heat at the low temperature heat exchanger 92. The continuous repetition of this cycle generates refrigeration at the low temperature heat exchanger 92. The operation of the pulse tube refrigerator 80 thus functions as a cryogenic refrigerator to generate refrigeration.
The above device, however, has a drawback that the operation is not stable, due to a circulation flow of working gas in a direction determined by the various operational conditions in addition to the above reciprocal movement of the flow of the working gas. This is because the conventional pulse tube refrigerator 80 forms a closed loop by the pressure oscillator 81 and the refrigerating portion 82, one end (regenerator 91 side) of which is connected to the other side (high temperature heat exchanger 94 side) through the pressure oscillator 81.
It is an object of the present invention to provide an improved pulse tube refrigerator which obviates the above conventional drawbacks.
It is another object of the present invention to provide an improved pulse tube refrigerator which is stable in operation.
According to the present invention, the above and other objects are advanced by a pulse tube refrigerator which includes a refrigerating portion including a regenerator, a low temperature heat exchanger, a pulse tube and a high temperature heat exchanger fluidically connected in this order; first pressure oscillation means for generating pressure oscillations of a working fluid in the pulse tube, said first pressure oscillation means comprising a first compressor, a first high pressure supply valve, and a first low pressure supply valve, wherein the regenerator is connected with outlet and inlet ports of the first compressor via the first high pressure supply valve and the first low pressure supply valve, respectively; and second pressure oscillation means provided independently of the first pressure oscillation means for adjusting a phase difference between the pressure oscillation and displacement of the working fluid in the pulse tube, said second pressure oscillation means having a second compression source, a second high pressure supply valve, and a second low pressure supply valve, wherein the high temperature heat exchanger is connected with outlet and inlet ports of the second compressor via the second high pressure supply valve and the second low pressure supply valve, respectively.
Since the second pressure oscillation means for adjusting the phase difference between the pressure oscillation and displacement of the working fluid is provided independently of the first pressure oscillation means, the first end second pressure oscillation means and the refrigerating portion do not form a closed loop, thereby preventing an undesired circulating flow of the working fluid and keeping the device in stable condition.
According to another aspect of the present invention, the pulse tube refrigerator further includes a buffer tank connected to the high temperature heat exchanger and having an intermediate pressure which is between the outlet and inlet pressures of the first compressor for further adjusting the phase difference between the pressure change and position change of the working fluid in the pulse tube. The buffer tank having the intermediate pressure between the outlet and inlet pressures of the first compression source is provided to further finely adjust the phase difference therebetween.
This feature will reduce the load of the first and second pressure oscillation means by first reducing the pressure change between the minimum pressure (inlet pressure of the first compression source) and an intermediate pressure (buffer tank pressure) at the pressure increasing operation of the working fluid in the pulse tube, and then increasing the pressure to the maximum pressure (outlet pressure of the first compression source) by opening the first high pressure supply valve.
According to a further aspect of the present invention, the buffer tank and the refrigerating portion are connected through a buffer side valve. This feature will also reduce the load of the first and second pressure oscillation means by first reducing the pressure change between the maximum pressure (outlet pressure of the first compression source) and the intermediate pressure (buffer tank pressure) at the pressure decreasing operation of the working fluid in the pulse tube, and then reducing the pressure to the minimum pressure (inlet pressure of the first compression source) by opening the first low pressure supply on-off valve.
According to still further aspect of the present invention, the opening state of the first high pressure supply valve is overlapped with at least a part of the opening state of the second high pressure supply valve at a pressure increasing stage of the working fluid in the pulse tube.
Since the opening state of the first high pressure supply valve is overlapped with at least apart of the opening state of the second high pressure supply valve at a pressure increasing stage of the working fluid in the pulse tube, working fluid, the pressure of which reaches the maximum level (outlet pressure of the first compression source), is flowing into the outlet port of the second compression source in its position change.
The generation of the pressure of the second compression source is assisted by the working fluid flowing into the outlet port to reduce the power or load needed et the second compression source.
According to still further aspect of the present invention, the opening state of the first low pressure supply valve is overlapped with at least a part of the opening state of the second low pressure supply valve at a pressure decreasing stage of the working fluid in the pulse tube.
Since the opening state of the first low pressure supply valve is overlapped with at least apart of the opening state of the second low pressure supply valve at a pressure decreasing stage of the working fluid in the pulse tube, working fluid, the pressure of which reaches the minimum level (inlet pressure of the first compression source), is flowing into the inlet port of the second compression source in its position change.
The generation of the pressure of the second compression source is assisted by the working fluid flowing into the inlet port to reduce the power or load needed at the second compression source.
According to still further aspect of the present invention, the pulse tube refrigerator includes a refrigerating portion formed by a regenerator, a low temperature heat exchanger, a pulse tube and a high temperature heat exchanger in line in this order, a first compression source having an outlet port and an inlet port, a first high pressure supply valve via which the outlet port of the first compression source connects to the regenerator, a first low pressure supply valve via which the inlet port of the first compression source connects to the regenerator, a second compression source haying en outlet port end en inlet port, a second high pressure supply valve vie which the outlet port of the second compression source connects to the high temperature heat exchanger, and a second low pressure supply valve vie which the inlet port of the second compression source connects to the high temperature heat exchanger.
Since the first compression source is provided independently of the second compression source, a closed loop formation is not formed, and an undesired circulating flow of the working fluid is not generated. Therefore, it is possible to keep the device in stable condition.